Cathode ray tube mesh assembly supported between envelope sections



Nov. 8, 1966 Ffca. OESS 3,284,655

CATHODE RAY TUBE MESH ASSEMBLY SUPPORTED BETWEEN ENVELOPE SECTIONS Filed June 10, 1965 2 Sheets-Sheet 1 ZZZ-a5 Nov. 8, 1966 F. G. 0555 3,284,655

CATHODE RAY TUBE MESH ASSEMBLY SUPPORTED BETWEEN ENVELOPE SECTIONS Filed June 10, 1963 2 Sheets-Sheet Ana/Wm. 52037.4( 6. 0:35,

Zmmq+ Maya/4% United, States Patent 3,284,655 CATHODE RAY TUBE MESH ASSEMBLY SUP- PORTED BETWEEN ENVELOPE SECTIONS Frederick G. Oess, Oceanside, Califl, assignor to Hughes Aircraft Company, Culver City, Calif., a corporation of Delaware Filed June 10, 1963, Ser. No. 286,568 2 Claims. (Cl. 313-286) This invention relates to electronic vacuum tube apparatus and to means and methods for mounting electrode structures therein. More particularly, the invention relates to cathode ray tubes of the direct-viewing storage type and to means and methods for mounting mesh storage targets and the like therein.

There are many types of cathode ray tubes in which a target structure comprising a metallic mesh or screen must be mounted radially across the tube envelope so as to be substantially normal to the tube axis. While description herein will be principally with respect to directview storage tubes, it will be understood that this is by Way of example only and that the invention may be practiced to advantage in other types of cathode ray tubes such as frequency scan converters, for example. In direct- 'v1ew storage tubes a mesh target is provided in order to provide a storage surface capable of retaining a charge pattern thereon for the purpose of controlling the passage therethrough of electrons. In general, such tubes utilize one or more electron guns for scanning the storage target to thereby establish a desired charge pattern in accordance with information signals. This charge pattern in turn controls the passage of a flood beam of electrons which cover the storage target in blanket fashion and are able to penetrate through the interstices of the mesh wherever a positive potential storage charge obtains, for example. Many direct-view storage tubes of this type utilize the phenomena of secondary emission from a coating on this storage tube mesh to permit electrical charging of the coating by the scanning electron beam. The secondary electrons thus emitted from the storage target must be collected. It is customary that these secondary electrons be collected by a collector screen or mesh likewise mounted within the tube envelope and extending radially thereacross parallel and adjacent to the storage target mesh. It is also desirable in some instances to provide still another screen in such tubes for the purpose of repelling ions away from the storage target which would otherwise cause an undesired charging of the storage target by ion currents.

In the past, the practice has been to mount such screens or meshes on relatively rigid support rings usually of stainless steel which rings are then fastened by multiple 'insulated pin structures into the tube envelope. Such ring structures for mounting mesh targets are shown in Patent No. 2,928,970 to K. R. Hesse and assigned to the instant assignee. It will be appreciated that the use of such ring supports protruding into the chamber of the tube envelope reduces the total area available within the tube envelope for target purposes. In addition, where more than one such mesh is to be mounted in the envelope fabrication must be sequential; that is, the innermost mesh and ring must be secured in place to the insulated pins in the tube envelope as by welding or the like followed by a similar mounting of the additional screens. It will be appreciated that accurate spacing and alignment are to a large extent determined by the skill of the fabricator. Also, such structures add to the expense of manufacture because of the dependence upon the operators skill and the sequential assembly technique required. Furthermore, the inclusion of support rings protruding within the tube envelope make it more difficult to outgas the tube. If magnetic materials are used for such support structures, then distortion of slow moving electron beams such as flood electrons in storage tubes results. Such extraneous magnetic materials may also adversely effect the precise register of the higher velocity writing beams.

It is, therefore, an object of the present invention to provide an improved cathode ray tube apparatus and mesh target assembly therefor.

Another object of the invention is to provide an improved cathode ray tube apparatus having mesh target structures therein without having support rings and the like protruding within the evacuated chamber of the cathode ray tube.

These and other objects and advantages of the invention are realized by mounting and securing the periphery of a mesh target to a support ring and then mounting the ring substantially entirely within the wall of the tube envelope. The tube envelope initially comprises two separate portions which are sealed to each other with the ring which supports the mesh being disposed between these envelope portions.

The invention will be described in greater detail by reference to the drawings in which:

FIGURE 1 is an elevational View of the end portion of a cathode ray tube envelope showing mesh targets mounted therein according to the invention;

FIGURE 2 is an elevational view in section showing in detail the mounting of a mesh target assembly between portions of the wall of the tube envelope with an electrode connection to the target assembly;

FIGURE 3 is a plan view of a mesh target assembly in accordance with the invention;

FIGURE 4 is a partial plan View in section showing a mesh target assembly mounted into the wall of a tube envelope according to the invention and the method of making an electrode connection to the screen; and

FIGURE 5 is an elevational view partly in section of a direct view cathode ray storage tube embodying mesh target structures according to the invention.

Referring now to the drawings and to FIGURES 1 and 2 in particular, the invention will be described in connection with the fabrication of a direct view storage tube having a storage target therein. In FIGURE 1 is shown a section 2 of the cylindrical envelope for forming the ultimately evacuated chamber of such an electronic vacuum tube. The section 2 comprises a first envelope-forming member 4 having an end-plate 6 usually termed the faceplate. The envelope section 2 may also include second and third envelope-forming members 12 and 14. A viewing screen (not shown) comprising a layer of phosphor material may be disposed on the inside surface of the face plate 6 as is common practice in visual display cathode ray tubes. According to the invention the storage target 8 may comprise a substantially planar screen having 250 or more meshes per inch and a coating of dielectric material (not shown) such as magnesium fluoride disposed on one surface thereof. The storage dielectric coating is generally disposed on the surface facing the electron gun structure which is provided in the neck portionat the other end of the tube envelope (not shown).

The storage screen 8 may be circular and have a diameter greater than the internal diameter of the cylindrical envelope section 2 of the cathode ray tube. In practice a screen having a diameter about equal to the outside diameter of the envelope is utilized in order to facilitate the positioning of the screen during the subsequent processing and mounting thereof in the envelope wall. The screen is affixed to a circumferentlal ring 22 whose internal diameter preferably exceeds the inside diameter of the tube envelope section 2. The out- ,side diameter of the ring 22 may 'be about equal to or less than the outside diameter of the envelope section 2 so as to not protrude outside the envelope after having been permanently secured in place in the envelope wall. Before mounting the target 8 in position across the open end of the tube envelope member 4, for example, glass frit, which may be in powdered form, is applied over the edge portions of the envelope wall member thereat. It may be desirable to pre-wet or coat the edge of the tube envelope member 14, for example, which is to be joined to the envelope member 4. The target 8 is then placed in position across the envelope member 4 with the support ring 22 contacting the edge thereof. The envelope member 14 may then be mounted in place over and in contact with the ring 22 of the target 8 so that the edge portions of the envelope members 4 and 14, for example, may abut and be hermetically joined or sealed by heating the assembly in an inert or non-reducing atmosphere such as dry nitrogen, for example. As used herein the term abut is intended to mean touching and near-touching and includes overlapping and non-overlapping arrangements although overlapping configurations may not be particularly desirable.

In a typical application, a tube envelope of soft glass, such as Corning glass #0120, made and sold under this designation by the Corning Glass Works of Corning, New York, was employed. The envelope members were sealed by heating the assembly for one hour between 420 and 440 C. It is preferable to preheat the assembly to these temperatures at the rate of 3 per minute and to allow the assembly to cool at the same rate in order to avoid shock and stress to the glass.

The frit used to achieve the seal may be any low temperature sealing glass which has a coefficient of thermal expansion substantially equal to that of the envelope glass. Such frits are well known and are commercially available as solder glass and may comprise powdered glass dispersed in a binder such as amyl acetate to provide a powdered glass adhesive material of paint-like consistency.

As suggested previously it may be desirable to incorporate two or more target structures within a cathode ray tube envelope. The manner in which this may be achieved according to the present invention is also shown in FIGURE 1, wherein an additional screen target 10, which may be a collector electrode for example, is provided. Where such multiple screen target structures are to be provided, one may be placed over the open end of the envelope member 4 containing the faceplate portion 6 as described previously, while the other target structure, such as the collector electrode 10, may be disposed over the open end of the matching envelope member 12. After the application of the powdered glass adhesive or frit at the proper edge portions of the envelope members, a third envelope member 14 of the same material as the envelope members 4 and 12 may be disposed between these envelope members with their edge portions abutting as shown. The edge portions of the envelope member 14 may also be precoated with the powdered glass adhesive. The assembly is then fused and sealed by heating as described previously. The use of such a third envelope member 14 permits accurate and automatic spacing between the screen structures and this envelope member is therefore called a spacer ring.

In most cathode ray tubes employing such mesh target structures as described, it is desirable that external electrical connections thereto be provided. This may be accomplished as shown in FIGURES 2 and 4. The electrical connection, which may constitute a wire 16, is placed between abutting edge portions of the envelope members and in contact with the ring support portion 22 of the desired screen target such as the storage screen 8, for example. In order to enhance such contact the wire may be provided with an angled portion 16' which also facilitates anchoring the wire during and after the sealing operation. It may also be desirable to include a conductive frit 18 in the seal area to ensure good electrical connection between the wire 16 and the ring support member 22. Such conductive frits are well known and may comprise a mixture of finely divided gold or silver and the solder glass described previously. Except for the incorporation of the conductive frit 18, the sealing of the screen structures into the envelope wall may be accomplished with the use of the glass frit 20 as described previously.

It may also be generally desirable to bevel the edges of the envelope members and/or spacer ring member 14 to be joined as shown in FIGURE 2. Such bevelling is employed to avoid sharp glass corners which might constitute stress points adding to the fragility of the seal. The formation of excessive frit overhang or beads is also prevented or reduced by such beveling.

Referring now to FIGURE 5 a cathode ray structure is shown utilizing mesh target structures according to the invention. A cathode ray tube envelope 30 is shown comprising a smaller diameter neck portion 32 in which one or more electron guns may be disposed. As is common practice the cathode ray tube 30 also includes a relatively large diameter bulb portion 34 which is an integral part of the neck portion 32. On the inner surface of the faceplate 36 may be disposed a phosphor material constituting a viewing screen 38 as is well known. Adjacent and in contact with the viewing screen 38 may be a conductive layer 40 accelerating electrons to the viewing screen 38 and also constituting an electronpermeable light-reflecting coating. Adjacent to but spaced from the metal layer 40 may be a mesh storage target 8 mounted directly into the tube envelope by means of an annular support ring assembly 22 all as described previously including the electrical lead-in 16 thereto. Likewise disposed adjacent the storage electrode 8 is a collector screen 10 mounted directly into the tube envelope by means of an annular support ring assembly 22' and provided with an electrical lead-in 17 in the same fashion as the electrical connection 16 to the storage target 8.

It will thus be appreciated that a much simpler and more rugged tube structure utilizing one or more mesh targets therein is provided according to the invention which structure lends itself more readily to easy and less critical operations in the fabrication and assembly thereof.

What is claimed is:

1. In an electronic vacuum tube of the type having a mesh target disposed therein, the improvement comprising: at least a pair of envelope members having adjacent beveled edge portions and defining a chamber therewithin, a mesh target assembly disposed in and across said chamber and having a mesh portion secured to imperforate peripheral portions, said imperforate portions of said target assembly being disposed between said beveled edge portions of said envelope members, electrical lead-in means external to said chamber extending between said beveled edge portions of said envelope members and electrically connected to said imperforate peripheral portions of said target assembly, and sealing means disposed in and filling the space between said beveled edge portions of said envelope members thereby hermetically joining said envelope members and securing said target assembly and said electrical lead-in means thereto.

2. In electronic vacuum tube apparatus: at least first, second and third envelope members defining a chamber therewithin and having adjacent beveled edge portions, first and second mesh target assemblies having imperforate peripheral portions disposed in and across said chamber, the irnperforate peripheral portions of said first target assembly being disposed between the beveled edge portions of said first and second envelope members, the

imperforate peripheral portions of said seoiid target assembly being disposed between the beveled edge portions of said second and third envelope members, sealing means disposed in and filling the space between said beveled edge portions of said envelope members, all of said beveled edge portions of said envelope members being hermetically joined by said sealing means to thereby support said target assemblies, and electrical lead-ins means extending between beveled edge portions of said envelope members and electrically connected to respective ones of said imperforate peripheral portions of said target assembly and likewise being hermetically joined to said beveled envelope members.

References Cited by the Examiner UNITED STATES PATENTS Trump et a1. 3l3253 X McCarthy 313249 Klopping 313-253 X Dorgelo 313286 X Harris 313-348 X Nekut et al 3l3253 X Antoniades 313348 JAMES W. LAWRENCE, Primary Examiner.

R. SEGAL, Assistant Examiner. 

1. IN AN ELECTRONIC VACUUM TUBE OF THE TYPE HAVING A MESH TARGET DISPOSED THEREIN, THE IMPROVEMENT COMPRISING: AT LEAST A PAIR OF ENVELOPE MEMBERS HAVING ADJACENT BEVELED EDGE PORTIONS AND DEFINING A CHAMBER THEREWITHIN, A MESH TARGET ASSEMBLY DISPOSED IN AND ACROSS SAID CHAMBER AND HAVING A MESH PORTION SECURED TO IMPERFORATE PERIPHERAL PORTIONS, SAID IMPERFORATE PORTIONS OF SAID TARGET ASSEMBLY BEING DISPOSED BETWEEN SAID BEVELED EDGE PORTIONS OF SAID ENVELOPE MEMBERS, ELECTRICAL LEAD-IN MEANS EXTERNAL TO SAID CHAMBER EXTENDING BETWEEN SAID BEVELED EDGE PORTIONS OF SAID ENVELOPE MEMBERS AND ELECTRICALLY CONNECTED TO SAID IMPERFORATE PERIPHERAL PORTIONS OF SAID TARGET ASSEMBLY, AND SEALING MEANS DISPOSED IN AND FILLING THE SPACE BETWEEN SAID BEVELED EDGE PORTIONS OF SAID ENVELOPE MEMBERS THEREBY HERMETICALLY JOINING SAID ENVELOPE MEMBERS AND SECURING SAID TARGET ASSEMBLY AND SAID ELECTRICAL LEAD-IN MEANS THERETO. 